Vibratory systems and methods for packing foundry sand into a pattern prior to the pouring of molten metal have been in use for many years. One such system and method is described in Musschoot U.S. Pat. No. 4,454,906. Such a system is used for the casting of molten metal where a pattern embedded in sand is used to determine the shape into which the molten metal is formed. To ensure that the foundry sand fully penetrates all cavities and recesses of the pattern, a mold flask containing the pattern and sand is vibrated at controlled frequencies and strokes to produce accelerations in excess of gravitational acceleration to cause the sand to penetrate and completely fill all cavities, etc., in the pattern and then the accelerations are reduced to produce an acceleration less than the acceleration due to gravity to compact the sand in place. These systems are commonly referred to as lost foam integrated compaction systems.
Such known systems provided acceleration as by vibrating a vibratory table on which the mold flask is supported. Certain systems utilize a manual control to vary the speed of the motor to control acceleration. Alternatively, systems have been used which sense acceleration of the vibratory table and automatically control acceleration by controlling the speed of the motor responsive thereto.
It has been proposed that prior control systems do not provide adequate control, particularly in applications where the flask is loosely supported on the table. This results because acceleration of the vibratory bed may be different from the acceleration of the flask itself. Even in applications in which the flask is secured to the bed, the control may be less than ideal. Particularly, in such a system the critical element to be controlled is the sand, rather than flask. The vibratory table is merely a reference point. Although movement of the table is related to sand movement, it is not wholly accurate.
The present invention is intended to overcoming these and other problems associated with the prior control systems.